1. Field of the Invention
The present invention relates to improvement of a device for starting an AC load powdered by supply, an AC generator driven by either an engine or a motor.
2. Description of the Prior Art
It is well known that, when an AC load is started by the use of, as a power supply, either an engine generator or a motor generator, especially in case the load has lagging power factor such as an induction motor or an AC arc welder, the terminal voltage of the generator exhibits an abrupt large drop.
Generators of this type are usually provided with an automatic voltage regulator to regulate voltage drops due to load fluctuation. However, such automatic voltage regulator cannot fully counteract the abrupt and large initial voltage drop.
For the above-said reason, it has been practiced in general to use a generator having a capacity large enough to compensate for the voltage drop at the start. However, such counter-measure leads to expansion in the size of the system and increased cost.
In order to improve the above-mentioned inconvenience and disadvantage, there has been proposed and known a method of saturating the magnetic circuit of a generator by such means as a saturating coil prior to starting, and of starting the load in this state.
This known method is such that the load is started at the moment that the terminal voltage of the generator has temporarily leaped up to the non-loaded voltage by saturation of the magnetic circuit. Accordingly, it is possible to reduce the initial voltage drop supplied to the load which is connected to the generator and to thereby elevate the voltage supplied to the load. In order to insure this pattern of operation, however, it is necessary that, at the moment of energization of the starter, the saturating coil is still connected to the generator. Because of this, the current flowing through the saturating coil will momentarily overlap the current of the starting coil on the power supply side at the moment this starting coil is energized. Moreover, the initial current of the starting coil has a surge current characteristic for the period of 1 to 3 Hz. The overlap value of this surge current of the starting coil and the current of said saturating coil is intensive and momentarily causes a drop in the terminal voltage of the generator, giving rise to possible adverse effect on other related loads.